Cellular compartmentation in arginine metabolism of Neurospora will be studied in two respects. 1. The enzyme carbamyl phosphate synthetase A is an arginine-biosynthetic enzyme located in mitochondria. It is highly pegulated and has two subunits. We will study the structure, subunit regulation, aggregation and insertion into the mitochondria as factors in the control of enzyme activity. 2. Basic amino acids, such as arginine, are sequestered in vesicles in Neurospora cells, and serve as reservoirs and regulators of amino acid metabolism. We will complete the physical chemical and enzymatic characterization of the purified vesicles, and study the changes we can cause by genetic and physiological manipulations. The information gained in both parts of the project are applicable to mammalian cells, which show similar compartmental phenomena in the arginine pathway.